MAX-DOAS spectrometers are ground-based remote sensing instruments operating in the UV–visible spectral range and widely used for air quality observations. Through dedicated ESA activities, MAX-DOAS has been incorporated…
into the Fiducial Reference Measurements (FRM) framework, with the aim of harmonising instrumentation and data processing. This has led to the definition of best practices for instrument operation and the development of a prototype centralised processing system capable of delivering near-real-time
data. This system was successfully demonstrated in the FRM4DOAS project. For routine satellite validation, such as for Sentinel-5 Precursor, timely and operational access to high-quality FRM datasets from ground-based MAX-DOAS instruments i